This invention relates generally to battery separators and more especially to battery separators for lead-acid batteries.
Conventional separators used in lead-acid storage batteries have been provided with spacers such as glass mats (see FIG. 7), armour ribs (see FIG. 8) and projections in order to have enough electrolyte maintained between the negative and positive plate, to retard active material shedding in positive plates and to retard active material expansion in negative plates. The spacers add additional cost to the battery separator, therefore, such a storage battery has been high in cost. Corrugated type separators (FIG. 9) are also known and have some advantage in that they do not require extra, special spacing structure. However, corrugated type separators can only be used with rigid separator materials. For thin thermoplastic sheets, the corrugated type separators do not usually offer enough rigidity to withstand the pressure from the positive and negative plates and prevent negative material expansion.
The battery separator shown in FIG. 10 is that of U.S. Pat. No. 4,072,802 and its continuation U.S. Pat. No. 4,153,759. This battery separator overcomes some of the defects mentioned above. However, during embossment it proved necessary to at least partially melt the projecting parts, rendering them filmy and clogging the pores increasing electrical resistance. The channels providing for gas relief are side channels below the apex or vertically highest point of the embossments on the battery separator face when the battery separator is engaged in a battery. Thus gas can lodge below the embossments. Even if the embossments were to be medially penetrated, which they are not, to release the gas, a 0.degree. from the horizontal point would always exist at the bottom of any wall that did not extend all the way to the bottom of the battery separator face and a gas bubble could lodge below this point and linger there cutting off effective battery plate surface. Additionally because neither face of the battery separator of FIG. 10 has a continuous engagement with a battery plate from the top to the bottom of the battery separator face the embossed configuration retention is not as stable.
The present invention overcomes the above defects and gives battery separators having ideal characteristics.
One object of the present invention is to provide a high performance battery separator formed from a small pored, thin thermoplastic sheet.
Another object of the present invention is to provide a storage battery of a high performance and long life.
Yet another object of the present invention is to provide a battery separator that is easy to make and low in cost.
A still further object of the present invention is to provide a battery separator that has the lowest possible electrical resistance and the best possible gas relief characteristics.